Cupramine (ie Copper) will NOT killy the Ich parasite on the fish. It only kills the parasite in the free swimming stage when hatched from the cyst that falls off the fish.
This free swimming stage can take up to 28 days once the parasite drops off the fish.
You therefore, need to have the proper strenght of copper in the tank for at least 28 days once all spots on the fish are gone.
I hope you are testing for copper to make sure it is at 0.5ppm.
http://www.fishvet.com/no-ich_faqs.htm
"What is the life cycle of this parasite?
The life cycle of Cryptocaryon can be conveniently divided into four basic stages. Susceptible marine fish become infected with the active free-swimming stage, called the tomite.
The free swimming tomite has less than 12 hours to find and invade a host fish otherwise it will exhaust its energy reserves and die.
If an invasion is successful, the tomite penetrates below the skin and transforms into the parasitic stage which is known as a trophont. The trophont actively feeds on the fish's tissues, twisting and rotating as it does so. It grows rapidly, doubling in size approximately every 24 hours. By 48 hours, the parasitic trophont is just visible to the naked eye, appearing as a small white spot on the fish. By the third or fourth day of infection, the trophont has attained 3 to 5 millimeters in length and about this time it exits from the fish and drops down to the substrate.
Within a few hours the trophont has firmly attached to the substrate, forming a thick walled cyst. The cyst, known as a tomont, is the reproductive stage which will eventually give rise to between 100 and 300 infective tomites, thereby completing the life cycle.
Of course, not all tomites are successful in locating and infecting a host, even under ideal conditions only about 5 - 10% succeed. Nevertheless, within a closed environment, Cryptocaryon can increase in numbers by approximately tenfold every six to eight days. This enormous reproductive potential explains the sometimes rapid build-up of infection levels in any closed system."
